1. Field of the Invention
This invention relates to vehicles incorporating a handlebar steering arrangement and, more particularly, to vehicles such as bicycles in which the handlebars serve to provide partial support to the rider.
2. Description of the Related Art
The history of the bicycle goes back nearly 200 years; pedal operated bicycles, about 150 years. Variations of the current design have been in use for approximately 100 years, the main features of which are two medium sized wheels of approximately equal diameter, a chain drive to the rear wheel, rubber tires and wire spoke wheels. The frames are formed of thin tubing arranged in a diamond or triangulated design in which all tubes are subject to compression forces only so that lightweight tubing can be used.
Throughout much of its history, the bicycle has been used, both as a means of transportation and for sport and recreation, on paved roads or other relatively smooth surfaces. In the main, the commonly adopted spring support of the bicycle seat, coupled with the resilience afforded by pneumatic rubber tires, has provided sufficient resiliency to make the transmission of roadway shocks acceptable to the rider. From time to time efforts at improving the springiness of the bicycle have been proposed. These have taken the form of shock absorbers in the front fork and frame member, in the seat post, and in the rear suspension. There have also been various arrangements proposed to alleviate the rigidity of the support mounting of the front handlebar, since this is particularly related to the ability of the rider to control the bicycle, particularly over uneven terrain.
One of the earliest known arrangements for absorbing jars and shocks communicated to the handlebar of a bicycle during riding movement is disclosed in U.S. Pat. No. 583,483 of Kellogg, which discloses a spring within the post extending upward from the front fork in which the handlebar is pivotably mounted. This spring biased the mounting pivot so that some rotation of the handlebar about the pivot axis was permitted when shocks were encountered. An adjusting bolt permitted variation in the compression of the spring so that the softness of the ride might be controlled. Similar spring and pivoting arrangements for handlebar support mechanisms for use in bicycles, motorcycles and the like are disclosed in U.S. Pat. Nos. 1,468,835 of Rosen and 1,616,021 of Arzens.
E. K. Kuhn, in U.S. Pat. Nos. 1,640,454 and 2,324,403, discloses spring support arrangements for pivotable mounted handlebars of bicycles, motorcycles and the like in which a plurality of springs are used to provide the resilient support. In the arrangement of the later patent, Kuhn also incorporates a number of linkages coupled at a plurality of pivot points to provide resilient handlebar support in both upward and downward displacement from a rest position. In addition to being cumbersome and relatively costly to manufacture, these arrangements appear to present problems in maintaining proper stem alignment during negotiation of uneven terrain.
U.S. Pat. No. 1,183,389 of MacLean discloses a shock absorber for motorcycle handlebars in the form of a parallel bar linkage arrangement including a pair of helical springs mounted in compression between the ends of different arms of the linkages conceptually resembling somewhat the arrangement of the later Kuhn patent. In the MacLean arrangement, the handlebar support pivot element is completely separate from the stem extending to the front fork, being held together therewith by the shock absorber linkage. Like Kuhn, this arrangement is considered to be subject to substantial instability in stem alignment and steering control, in addition to adding weight and complexity which is unacceptable in a lightweight vehicle such as a bicycle.
Another adjustable shock absorbing handlebar structure which is particularly adapted for use on motorcycles employed in racing over rough and uneven terrain is disclosed in the Finkle U.S. Pat. No. 4,420,989. This uses an unconventional handlebar structure comprising parallel linkages extending from the handle grip members to a central structure which is attached to the fork. The grips and angulation of these parallel linkages are manually adjustable. The central portion of this arrangement contains a combination of resilient pads and a fluid-containing shock absorber which controls the pivoting of the parallel bar linkages and thereby the resilience of the grip members. This appears to be clearly unsuited for incorporation in a lightweight bicycle.
Still another adjustable shock absorbing handlebar structure, which has been marketed commercially, incorporates a two-piece gooseneck, comprising a base member that clamps to the stem extending upwardly from the front forks of the bicycle and a knuckle member that clamps to the handlebars. These two members are pivotably joined by a knuckle pivot pin. An offset spring support member in the form of a threaded rod with an adjustable retaining arrangement for a compression spring extends between the base and knuckle parts of the assembly. The rod has an eye portion which is pivotably mounted to an offset portion of the base. The other end of the rod couples to an offset portion of the knuckle in an arrangement which permits relative rotational and longitudinal movement between the two offset portions. This end of the rod also supports the compression spring which bears against the knuckle to bias the handlebar mounting to an upper rest position. The connections of the base and knuckle members to the rod and spring could be interchanged, if desired. Downward force against the handlebars, as when the rider encounters a bump at the front wheel, serves to compress the spring and pivot the handlebar mount downward, thus cushioning the bump and absorbing much of the shock which would otherwise be transmitted directly to the rider's arms and shoulders.
An article by Doug Roose entitled "Bicycle Suspensions," Bicycle Guide, August, 1988, pages 75-79, discusses the various problems of providing resilient support in bicycles which are subject to moderate to severe road vibrations and shock, such as may be encountered in off-road racing and BMX competition. Proposed solutions include resilient suspension arrangements for the front fork and the rear portion of the frame and a so-called shock stem for handlebar suspension which utilizes a block of rubber for cushioning. Further details regarding the construction of the shock absorbing handlebar stem are not disclosed.
In the past decade or two, off-road bicycle riding has become more popular as a recreational sport. The advent of production of the so-called "mountain bike", which is a beefed-up version of the bicycle design which was in common use before the trend to ultra-lightweight, thin-tired, multi-speed bicycles developed, with large balloon tires and reduced sprocket ratios in the propulsion system. The riding of such bicycles on mountain trails, particularly in a downhill run, requires precise steering control of the front wheel from the handlebar for safe riding. This requirement is intolerant of any "slop" or play in the types of support structure between the handlebar and the front wheel such as are presented by a number of the shock absorbing arrangements of the patents discussed hereinabove.